In recent years, a computerization of auxiliary machines such as an idling stop system, an air conditioner, a brake, a power steering, and the like has been advanced, the reliability of the lead acid battery is demanded ever more, and a technique for accurately detecting a charged state and a deteriorated state of the lead acid battery has become necessary. For example, in a liquid type lead acid battery, there has been a structure in which a liquid surface sensor and a liquid surface detecting circuit are attached to a container lid, for detecting whether or not the liquid surface of an electrolyte solution filled in a cell chamber of a container becomes lower than a predetermined height, at a time of a maintenance operation, and an alarm apparatus such as a buzzer, a lamp, or the like is activated in the case where the liquid surface of the electrolyte solution becomes lower than the predetermined height (for example, see Patent Documents 1 to 3).
An example of the lead acid battery is shown in FIG. 15. The lead acid battery is structured such that a liquid surface sensor installation portion 2a is provided in a container lid 2 covering an upper end portion of a container 1, a liquid surface sensor 3 is installed to the liquid surface sensor installation portion 2a, a recessed portion 2b is formed in the container lid 2, and an electronic circuit board 4 is contained in the recessed portion 2b. Further, positive and negative terminals 5 and 6 of the lead acid battery protrude from an upper face of the container lid 2.
The liquid surface sensor 3 is a sensor detecting whether or not the liquid surface of the electrolyte solution filled in the cell chamber of the container 1 is equal to or higher than the predetermined height, and the electronic circuit board 4 is a board mounting a liquid surface detecting circuit detecting the fact that the liquid surface of the electrolyte solution has become lower than the predetermined height based on the sensor signal from the liquid surface sensor 3. Further, an LED 4a and a buzzer 4b giving an alarm in the case where the liquid surface detecting circuit detects the fact that the liquid surface of the electrolyte solution has become lower than the predetermined height is mounted to a face of the electronic circuit board 4, and a switch 4c turning on and off an electric power supply of the liquid surface detecting circuit is also mounted thereto. The recessed portion 2b containing the electronic circuit board 4 is appropriately covered by a recessed portion lid or filled with a resin.
A lead wire 3f is derived from the liquid surface sensor 3, and the structure is made such that a sensor signal is outputted by connecting the lead wire 3f to the electronic circuit board 4. Further, connection rings 7 and 7 are connected respectively to terminals 5 and 6 protruding from the top face of the container lid 2, and the structure is made such that electric power is fed by connecting lead wires 7a and 7a derived from the connection rings 7 and 7 to the electronic circuit board 4.
However, when the lead wire 3f of the liquid surface sensor 3 and the lead wires 7a and 7a of the connection rings 7 and 7 are connected to the electronic circuit board 4, the lead wires 3f and 7a pass through the top face of the container lid 2. Accordingly, the lead wires 3f and 7a catches on an object at a time of transporting the lead acid battery or are sandwiched by a fixture at a time of installing the battery to a motor vehicle or the like, and there is a risk that the lead wires are disconnected. Further, there is a problem that if the electrolyte solution is spotted on the top face of the container lid 2, there is a risk that it is corroded. Further, there is a problem that an outer appearance is not good. Accordingly, in order to prevent the disconnection caused by the catching on of the lead wires 3f and 7a or the like, the structure may be made such that a groove is formed between the liquid surface sensor installation portion 2a on the top face of the container lid 2 or the terminals 5 and 6 and the recessed portion 2b, and the lead wire 3f and the lead wires 7a and 7a are fitted into the groove so as to be passed therethrough, however, even in this case, it is impossible to solve the problem of corrosion caused by the electrolyte solution. Further, it is impossible to solve the problem of unpreferable outer appearance.
Patent Document 1: Japanese Unexamined Utility Model Publication No. 05-015322
Patent Document 2: Japanese Unexamined Patent Publication No. 05-082174
Patent Document 3: Japanese Unexamined Patent Publication No. 05-074502